System Design

⏱ 3 min read Double-Entry Accounting Primer Every financial event produces at least two journal lines: one debit and one credit. The sum of […] Read article

⏱ 4 min read Overview A payout service disburses funds to recipients via multiple rails: ACH (batch, 1-2 day settlement), wire (same-day, high fee), Read article

⏱ 4 min read Feature Flag Targeting Service: Low Level Design A feature flag targeting service lets teams release features safely by controlling visibility Read article

⏱ 4 min read Experimentation Platform: Low Level Design An experimentation platform enables A/B and multivariate tests with rigorous statistical guarantees. This design covers Read article

⏱ 5 min read ML Model Serving Service: Low Level Design An ML model serving service provides versioned, low-latency online inference alongside batch prediction, Read article

⏱ 2 min read OT for Text Operations are insert(pos, text) and delete(pos, len). Transformation Function transform(op1, op2) adjusts positions of concurrent ops to Read article

⏱ 2 min read Cursor State { user_id, user_name, color, position: { line, col } // for text, or { x, y } for Read article

⏱ 3 min read Overview An ML-powered content moderation service classifies user-submitted content (text, images, video) at scale, routes borderline cases to human reviewers, Read article

⏱ 3 min read Quiz Engine Data Model A quiz engine supports timed assessments, randomization, auto-grading, leaderboards, and anti-cheat mechanisms. Core Tables Quiz (id, Read article

⏱ 4 min read Bookmark Service: Core Schema The bookmark service persists saved URLs with rich metadata and organizational structure. Bookmark Table id BIGSERIAL Read article

⏱ 4 min read Reading List Service: Core Schema The reading list service saves articles for later reading with content extraction and offline availability. Read article

⏱ 5 min read Content Archival Service: Storage Tiers The archival service manages long-term content retention across four S3 storage tiers with different cost Read article

⏱ 2 min read Data Model Dashboard Table Dashboard ( id, name, owner_id, layout JSONB, — grid positions created_at ) Widget Table Widget ( Read article

⏱ 3 min read Entity Types Nearby search must handle two fundamentally different entity classes: Static entities — restaurants, venues, stores; position rarely changes Read article

⏱ 3 min read Tile Coordinate System Map tiles use a Z/X/Y (zoom / column / row) scheme: Zoom 0 = 1 tile covering Read article